This invention relates to nonmagnetic steel having a low thermal expansion coefficient and a high yielding point and a method of manufacturing the same.
The field of application of nonmagnetic steel has been broadened in recent years, for example as structural materials for constructing magnetic floating type high speed railway (so-called a linear motor car), atomic reactors, various electric component parts or the like. Suitable nonmagnetic steel can be obtained by selecting its composition to have austenitic structure. Typical example of such a steel is austenitic stainless steel. In addition, Hadfield steel (containing 0.9.about.1.3% by weight of C and 11.about.14% by weight of Mn) is a famous one. In the following description, all percentages of the elements are % by weight based on the total weight of the nonmagnetic steel. As improvements thereof, such low carbon, high manganese nonmagnetic steels are known as Mn-Cr steel (for example DIN.times.40 Mn-Cr 18 steel), Mn-Cr-Ni steel (for example DIN.times.5 Mn Ni Cr 14 steel), and Mn-Cr-Ni-V steel (for example DIN.times.45 Mn Ni Cr V 1376 steel), etc.
The linear motor cars are prosperious in future and such railway system requires a large quantity of nonmagnetic steel as guideway structures or reinforcing steels for manufacturing railway beds so that addition of such expensive alloying elements as Ni and V is not advantageous. Such nonmagnetic steel is also required to have low thermal expansion coefficient and low electric resistivity in addition to nonmagnetic property. Moreover it is also required that the permeability should not increase even after cold working eg. However, the prior art nonmagnetic steel can not satisify these requirements.